The present invention relates to techniques for processing overhead bytes in a SONET or an SDH frame, and more particularly, to techniques for processing overhead bytes in a SONET or SDH frame away from the data path.
Synchronous optical network (SONET) and Synchronous Digital Hierarchy (SDH) are standards for data transmission across optical telecommunications networks. Data bits that are transmitted according to a SONET or an SDH standard are grouped into frames. The data bytes typically contain 8 data bits. The data bytes are typically grouped into words for internal processing. Any number of bits and bytes can form a word (e.g., 64 bits/8 bytes per word).
Each frame contains an overhead section and a payload section. The overhead section includes bits specified by a SONET protocol. The overhead section includes information that allows communications between an intelligent network controller and the individual nodes in the network. For example, the first two bytes (A1 and A2) in a frame are used to indicate the beginning of a SONET frame. The payload section includes the data bits that are being transferred from one location to another.
An STS-1 pointer (H1 and H2 bytes) allows the synchronous payload envelope (SPE) to be separated from the transport overhead bytes. The pointer is an offset value that points to the byte where the SPE begins. If there are any frequency or phase variations between the STS-1 frame and its SPE, the pointer value will be increased or decreased accordingly to maintain synchronization.
In prior art systems, the pointers and other overhead bytes are processed on the data path at the same data rate as data on the data path. The overhead bytes were processed using round-robin pipelined (time-sliced), replicated functions. Results are obtained every clock cycle and stored in pipelined flip-flops, or RAM, according to well known pipelining techniques.
Prior art systems used a substantial amount of circuitry to implement pipelining and replication to process the overhead bytes at the same data rate as the data path. Therefore, it would be desirable to provide techniques for processing overhead bytes in SONET frames that use less circuitry and provide more flexibility.